AttributeError: module 'pennylane' has no attribute 'matrix'

PennyLane Help
1

Hello! If applicable, put your complete code example down below. Make sure that your code:

  • is 100% self-contained — someone can copy-paste exactly what is here and run it to
    reproduce the behaviour you are observing
  • includes comments
def create_hamiltonian_matrix(n_qubits, graph, weights, bias):

    full_matrix = np.zeros((2 ** n_qubits, 2 ** n_qubits))

    # Creates the interaction component of the Hamiltonian
    for i, edge in enumerate(graph.edges):
        interaction_term = 1
        for qubit in range(0, n_qubits):
            if qubit in edge:
                interaction_term = np.kron(interaction_term, qml.matrix(qml.PauliZ)(0))
            else:
                interaction_term = np.kron(interaction_term, np.identity(2))
        full_matrix += weights[i] * interaction_term

    # Creates the bias components of the matrix
    for i in range(0, n_qubits):
        z_term = x_term = 1
        for j in range(0, n_qubits):
            if j == i:
                z_term = np.kron(z_term, qml.matrix(qml.PauliZ)(0))
                x_term = np.kron(x_term, qml.matrix(qml.PauliX)(0))
            else:
                z_term = np.kron(z_term, np.identity(2))
                x_term = np.kron(x_term, np.identity(2))
        full_matrix += bias[i] * z_term + x_term

    return full_matrix


# Prints a visual representation of the Hamiltonian matrix
ham_matrix = create_hamiltonian_matrix(qubit_number, ising_graph, target_weights, target_bias)
plt.matshow(ham_matrix, cmap="hot")
plt.show()

If you want help with diagnosing an error, please put the full error message below:

ttributeError                            Traceback (most recent call last)
Cell In[12], line 31
     27     return full_matrix
     30 # Prints a visual representation of the Hamiltonian matrix
---> 31 ham_matrix = create_hamiltonian_matrix(qubit_number, ising_graph, target_weights, target_bias)
     32 plt.matshow(ham_matrix, cmap="hot")
     33 plt.show()

Cell In[12], line 10, in create_hamiltonian_matrix(n_qubits, graph, weights, bias)
      8 for qubit in range(0, n_qubits):
      9     if qubit in edge:
---> 10         interaction_term = np.kron(interaction_term, qml.matrix(qml.PauliZ)(0))
     11     else:
     12         interaction_term = np.kron(interaction_term, np.identity(2))

AttributeError: module 'pennylane' has no attribute 'matrix'

And, finally, make sure to include the versions of your packages. Specifically, show us the output of qml.about().

Version: 0.18.0

2

Hey @Azadeh! Welcome to the forum :smiley:

Looks like your PennyLane version is way out of date! We’re on v0.31 now :sweat_smile:. This code

qml.matrix(qml.PauliZ(0))

works when you’ve upgraded. You can upgrade by doing:

pip install --upgrade pennylane

Hope this helps!